1. The Field of the Invention
The present invention relates to systems, methods and apparatus configured to implement a thermodynamic cycle via countercurrent heat exchange. In particular, the present invention relates to generating electricity by heating a multi-component stream with a heat source stream at one or more points in a thermodynamic cycle.
2. Background and Relevant Art
Some conventional heat transfer systems allow heat that would otherwise be wasted to be turned into useful energy. One example of a conventional heat transfer system is one which converts thermal energy from a geothermal hot water or industrial waste heat source into electricity using a counter current heat exchange technology. For example, the heat from relatively hot liquids in a geothermal vent (e.g., “brine”) can be used to heat a multi-component fluid in a closed system (a “fluid stream”), using one or more heat exchangers. The multi-component fluid is heated from a low energy and low temperature fluid state into a relatively high-pressure gas (“working stream”). The high-pressure gas, or working stream, can then be passed through one or more turbines, causing the one or more turbines to spin and generate electricity.
Accordingly, conventional heat transfer systems operate on the general counter current heat exchange principles to heat the multi-component working fluid through a variety of temperature ranges, from relatively cold to relatively hot. A conventional fluid stream for such a system comprises different fluid components that each have a different boiling point. Thus, one component of the fluid stream may become a gas at one temperature point, while another fluid stream component may remain in a relatively hot liquid state at the same temperature. This can be useful for separating the different components at different points in the closed system. Nevertheless, all, or nearly all, of the components of the fluid stream can be raised to a temperature such that all components of the fluid stream collectively comprise a “working stream”, or high pressure gas.
To accomplish heating of the fluid between the fluid stream and the working stream, the heat transfer system comprises apparatus configured primarily to cool the working stream to a cooler temperature, or heat the fluid stream to a hotter temperature. For example, the fluid stream passes through one or more heat exchangers that couple the fluid stream to the heat source stream as the fluid stream progresses toward a high temperature state, which is then passed through the one or more turbines. By contrast, the working stream that has already passed through the turbines is typically referred to as a spent stream. The spent stream is cooled by transferring heat to the fluid stream in a heat exchanger, since the spent stream is relatively hotter than the fluid stream at one or more stages in the system.
In order to achieve the temperature requirements for expansion in the turbines, countercurrent heat exchange systems heat the fluid stream from lower temperature points to the higher temperature points. This results in a number of system variables that conventional heat exchange systems will take into account. For example, if the optimal expansion temperature of an ambient temperature multi-component stream is a vapor working stream of a very high temperature, a very hot heat source that is typically much hotter than the desired temperature of the working stream will be utilized. Alternatively, if the heat source is only somewhat hotter than the ultimate desired temperature of the multi-component stream, the fluid stream will likely need to be warmer than ambient temperature, so that the multi-component fluid can be heated to the desired working stream temperature.
At least in part, due to this distinction in fluid stream starting temperatures, temperatures of the heat source, desired temperature of the working stream, and efficiencies of the system the heat source brine is usually discarded at a temperature that is much hotter than desired. For example, in some illustrative systems as conventional heat transfer systems pass the brine through one or more heat exchangers, the brine is cooled from an average temperature of about 600° F. to a throw-away temperature of about 170-200° F. While 200° F. is still a relatively hot temperature to perform meaningful heat transfers on conventional fluid streams, the conventional fluid stream is considered relatively cool, or lukewarm, at a similar temperature of about 170-200° F. In particular, the coolest point of a conventional fluid stream is usually too warm to be heated in any efficient way by the low temperature portion (i.e., the “low temperature tail”) of the brine. As such, conventional heat systems tend to be more efficient by discarding the brine at approximately 170-200° F.
One possible solution could be to cool the fluid stream to temperature that is much lower than 190-200° F., so that the fluid stream can be efficiently heated using the heat of the low temperature tail. In principle, this might involve the use of a Distillation Condensation Sub-system (“DCSS”) in conjunction with the above-described heat transfer system. Unfortunately, while use of a DCSS could efficiently cool a spent stream, the temperature to which the conventional DCSS would cool a typical spent stream would ordinarily be too low to be efficiently utilized. That is, the conventional DCSS would cool the spent stream to a temperature that is so low that it could not be efficiently raised to a high enough temperature later on as a working stream.
Accordingly, an advantage in the art can be realized with systems and apparatus that allow efficient use of a low temperature tail. In particular, an advantage in the art can be realized with heat transfer systems that are able to efficiently use a DCSS, so that a fluid stream can still be raised to an efficient working stream temperature.